1. Field of Invention
An embodiment of the present invention relates to a semiconductor memory device and, more particularly, to a semiconductor memory device including a plurality of memory cells.
2. Description of Related Art
A semiconductor memory is a storage device that is realized using a semiconductor such as silicon (Si), germanium (Ge), gallium arsenide (GaAs) or indium phosphide (InP). A semiconductor memory is divided into two types: volatile memory and nonvolatile memory.
Volatile memory is a memory that may lose its stored data when power supply is off. Examples of the volatile memory may include Static RAM (SRAM), Dynamic RAM (DRAM) and Synchronous DRAM (SDRAM). Non-volatile memory is a memory that may retain the stored data even when not powered. Examples of the non-volatile memory may include Read Only Memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable and Programmable ROM (EEPROM), flash memory, Phase-change RAM (PRAM), Magnetic RAM (MRAM), Resistive RAM (RRAM) and Ferroelectric RAM (FRAM). Flash memory is divided into NOR type and NAND type.
In order to have a higher integration degree of semiconductor memory devices, research has been conducted on semiconductor memory devices having a three-dimensional (3-D) array structure. A semiconductor memory device with a 3-D array structure is operated in a different manner from a semiconductor memory device with a two-dimensional array structure. Therefore, it is important to ensure characteristics of a semiconductor memory device having a 3-D array structure.